A prior art prepaid type portable telephone system proposed in JP-A No. 3-45031 is capable of metering message units used by a portable telephone and of stalling the portable telephone upon the detection of completion of a predetermined number of message units corresponding to a predetermined value to enable the omission of both a location registering operation and an accounting operation to be carried out by a switching system. The function of making message units correspond to a predetermined amount of money of the portable telephone is restored when the predetermined amount of money is paid.
The portable telephone for the prior art portable telephone system needs a circuitry for counting the number of message units, calculation and data storage to carry out an accounting procedure, and hence the complexity of the portable telephone is enhanced accordingly, which impedes the miniaturization and the reduction of weight of the portable telephone.
The accounting circuit of the portable telephone capable of carrying out an accounting procedure may be altered dishonestly, and it is difficult to prevent the dishonest use of the portable telephone.
The foregoing prepaid charging system cannot be applied to a simple portable telephone system. A portable telephone for a current portable telephone system is too expensive to use for the simple portable telephone system having a prepaid type charging system.
The present invention has been made to solve the foregoing problems and it is therefore an object of the present invention to provide a high-security portable telephone system allowing the use of a small, lightweight prepaid type portable telephone, and to provide a small, lightweight portable telephone for the portable telephone system.